1. Field of the Invention:
The present invention relates to a fixing roller and said fixing roller manufacturing process for a heat roller fixing device used in electrophotographic copying machines, facsimiles, printers and like machines using an electrophotographic process.
2. Description of the Prior Arts:
Conventional electrophotographic copying machine, heat roller fixing devices are known, like the device disclosed in Tokkai Sho 59-111177.
Conventional fixing devices comprise a heating roller incorporating a heater which have a separation layer on the electrically conductive core member. A pressure roller makes pressure contact with said heating roller, and an insulating roller on an electrically conductive core member. In such devices, copy paper, having a charged toner image thereon, pass between both rollers with the toner-bearing surface facing the heating roller, whereby the toner image is fixed onto the copy paper.
With this type of heat roller fixing device having a heat-fixing roller, the heated roller surface has sufficiently good release properties to prevent thermal adhesion of the toner without necessitating the application of silicone oil or a like offset preventing agent, or with use of only a very small amount of such agent. Thus, the copy paper feels pleasant to the touch.
However, the separation surface layer of the heated roller can be triboelectrically charged by the insulating surface layer of the pressure roller or by contact with the copy paper and as such is liable to electrostatically attract the toner and permit offset. This type of triboelectrically-induced offset cannot be prevented by the application of a offset preventing agent.
While it is known, as disclosed in Tokkai Sho 57-150869, that electrical resistance is reduced when a large amount of carbon black or other conductive substance is incorporated in the primer layer to prevent such charging if a large amount of carbon black, or like substance, is incorporated in the primer layer, the adhesive property of said primer layer is reduced and its essential function is lost. A further limitation is the occurrence of cracking in the thin primer layer caused by a large content of carbon black or like substance.
Another limitation of conventional devices employing resin powder coatings which incorporate large amounts of conductive substances applied over the primer, is the impossibility of effectively preventing triboelectrically-induced offset.